One of the main benefits of the growing trend towards modernization in industry is the opportunity to improve efficiency and cut costs, as production lines are refitted and new plants are constructed. With this thought in mind, the switch from traditional belt-driven or direct-coupled reducers to state-of-the-art gear motors is seen as a smart alternative by more and more mill managers.
The advantages are significant, not only from a capital and operating cost perspective, but because of the tremendous application flexibility that gearmotors offer. The evolution of gearmotor design, in combination with today's latest electronic drive technology, opens up possibilities that were simply not available in years past.
Conventional V-belt Applications
Traditionally, V-belt drives offered limited capabilities that addressed certain requirements within the industry. V-belts were most commonly used for reducing motor input speeds on specific reducer types, to keep them within their optimum operating range. In addition, they offered the flexibility to change or fine-tune speeds in the field after installation. By adjusting the belt drives, the number of gear ratios used throughout the mill could be reduced. And V-belts were sometimes considered an inexpensive method of protecting gear units in overload conditions.
Why Consider Eliminating V-belt Drives?
There are some good reasons for eliminating V-belt drives on the input side of reducers. Apart from the loss of horsepower and efficiency through belt slippage, V-belts impose overhung loads which can limit the longevity of motor/reducer bearings. Their limited flexibility cannot accommodate today's high stop/start cycling applications. And there are safety issues - not only must V-belts be replaced as they wear out, but when belt guards are removed, exposed V-belts are dangerous to maintenance personnel. Moreover, the relatively large dimensional envelope of the complete drive takes up considerable shop space.
Practical Advantages Of AC Gearmotors
By comparison, AC gearmotors offer numerous practical advantages. First and foremost, with modern helical gearing, gearmotors deliver dramatically better operating efficiency. Because overhung loads on the motor and reducer-shaft bearings are eliminated, service life is longer. The maintenance required to align belts and couplings is also eliminated, as are the safety concerns.
Today's compact AC gearmotor designs also save plant space, not to mention the capital and installation cost savings that result from smaller, less complicated mounting platforms. Furthermore, with most designs the motor and terminal box can be rotated to accommodate electric cable entry from any angle, an advantage in awkward locations.
Performance Advantages Of Fully Integrated Gearmotors
By far the best reason for making the switch to integrated AC gearmotors is performance. In a fully integrated gearmotor, the motor's low-inertia rotor is specifically matched to the characteristics of the gear unit. This results in high dynamic capability which is especially important for high stop/start cycling applications.
Also, the majority of today's gearmotors incorporate an integrated high-performance brake, ideal for applications requiring controlled deceleration of loads.
Another advantage of integrated gearmotors is that they are designed to work well with inverters. Using a gearmotor and variable phase converter in combination, along with closed-loop feedback by means of encoders mounted on the motor shaft, indexing and point-to-point positioning applications are possible.
Electronic drives also provide for fine tuning of speed and control, incorporating features such as overload protection and adjustable starting torques. However, advanced features notwithstanding, the biggest gains in performance come from unlimited combinations of motors and gear units that can be achieved.
Helical Gearmotors are the most widely used gear units. The typical configuration has two or three gear stages in a single housing. This makes the entire drive narrower and lower in height, allowing for greater space savings. The construction of these drives is simple yet robust, and easily meets the requirements of most applications.
Modular gearmotors come in numerous gearing configurations, depending on the criteria of the application. If extreme slow speed is required, a planetary combination helical gearmotor may be the answer. At the opposite end of the scale, a dynamic, high-speed application would require a low-backlash helical bevel reducer with a servomotor. The wide range of modular options available today offers customers a vast selection of pre-engineered drive solutions, to meet the exact requirements of even the most demanding applications.
In fact, the actual gearing is only part of the equation in arriving at the ideal drive system. Overall gearmotor performance is highly dependent on the design and operating characteristics of the motor. The correct synergy between gear unit and motor is critical in obtaining high cycling capability. Such favorable operating conditions require low rotor inertia, which is achieved by designing high-performance motors with smaller rotor diameters. Special design measures also need to be taken to reduce inrush currents, which lowers thermal stress and extends the life of the windings.
A wide variety of accessories are available to complement the application flexibility of today's gearmotors, such as brakes, backstop units, force ventilation, feedback units and temperature sensors, to name a few. Integration of these and other accessories is optimized through the gearmotor's modular design.
Modular gearmotors are used in both simple and complex applications, in almost all areas of industrial production, manufacturing and transportation. In addition to those discussed above, recent advances in gearing, motor design and inverter technology have made a large number of control and process functions available. The result has been the evolution of the intelligent geared motor.
Changing Views & Technology
For an example of making the shift from traditional drive technology to gearmotors, we turn to the sawmill industry. In the past, primarily due to the absence of any viable alternative, hydraulic and pneumatic drives have been used for cycling and positioning control. With the advent of today's gearmotor and VFD technology, improved efficiency for applications requiring high-cycling and positioning control can be achieved electronically. Equally important, initial costs are lower and payback is faster.
The most obvious reduction in operating costs is in energy savings. In order to supply the required pressure on demand, hydraulic systems must run continuously. This means the electric motors driving the hydraulic power units consume considerable energy, while a high percentage of the time they are not in productive use. In addition to the energy cost savings, one has to consider the complexity of the hydraulic circuitry and the regular maintenance required to maintain reliable operation. However, the energy savings alone makes implementing gearmotors with VFD control an extremely attractive option.
To put things in proper perspective, a local mill performed a study on converting their SC sorter/trimline from hydraulics to gearmotors and variable frequency drives. When they compared power consumption for both systems, they discovered that the gearmotor/VFD solution would save them approximately $21,000 per year - and that's just the energy savings. There were also important performance improvements in terms of higher sorter and trimline speeds that translated into higher production output per shift. The projected payback period was less than seven months.
Hydraulic vs. Gearmotor/VFD Cost Comparison
The ability of gearmotor/VFD systems to deliver capabilities such as programmable control for positioning, torque limiting and current limiting, for example, makes for an extremely reliable, low-maintenance alternative that can offer substantially greater uptime and improve the bottom line of any mill.
What's more, such features give gearmotor/VFD technology tremendous flexibility for solving existing production bottlenecks in mills, while offering designers a wide range of solutions when implementing new machinery. Of course everything we have discussed here applies equally to pneumatic systems. In the current market climate, high demand for efficiency, environmental issues, wildly fluctuating energy costs and even varying weather conditions can all have a negative impact on hydraulic and pneumatic systems - all good reasons to consider a total electronic solution.
The shift is occuring slowly but inevitably. The broader range of applications in the mill industry, combined with the need for greater versatility and control, is forcing operators to look for alternative drive solutions. At the same time, innovation in materials and technology is enabling drive manufacturers to develop industry-specific solutions, working with mill owners to optimize their applications as a viable means to diversifying their product mix, adding capacity and improving efficiency. Whichever way you cut it, the move to gearmotors is an important business decision that should not be overlooked.